Forty years after Gary Kildall released the first version of CP/M, the Computer History Museum in Mountain View, California has made the source code to several versions of the landmark eight-bit OS available as a free download from its website.
The code, which is written in a combination of assembly language and Kildall's homegrown PL/M, is archived as a 147MB Zip file that includes both ASCII source files and scanned printouts from the 1970s.
CP/M was a runaway success in the early days of the PC industry, owing largely to its portability, in an era when computer makers typically wrote operating systems to run on their own hardware only.
"Kildall's addition of the BIOS allowed not just IMSAI systems but all Intel 8080 and compatible microprocessor-based computers from other manufacturers to run same the operating system on any new hardware with trivial modifications that could be accomplished by a programmer in a few hours," the Computer History Museum's David Laws writes in a blog post celebrating the OS.
In addition, CP/M benefited from Kildall's early fascination with the floppy disk, which would eventually supplant tapes as the preferred storage medium for PCs.
CP/M's widespread adoption in turn spurred the growth of the commercial software industry, giving rise to some of the bestselling applications of the 1970s and 1980s, including dBase and WordStar.
The first version of CP/M shipped in 1974, and by 1982, Digital Research, the company Kildall founded to market the OS, employed more than 200 people and was said to bring in revenues of more than $20m per year.
But as rapid as CP/M's rise was, its decline was even faster. In 1981, seeing that IBM was having trouble negotiating a license from Digital Research to use CP/M in its new IBM PC line, Microsoft bought a CP/M lookalike called Q-DOS and licensed a reworked version of it to Big Blue as PC-DOS (and later to other PC clone makers as MS-DOS).
The rest is history. The IBM PC platform exploded, and by the mid-1980s, Microsoft's OS was outselling CP/M and Digital Research's own sales figures were rapidly declining, eventually to fade into oblivion.
Curious hackers who would like to see what the source code to such a relatively primitive operating system looks like can find the full download bundle – including code to versions 1.1, 1.3, 1.4, and 2.0, spanning from 1974 through 1979 – is available here.
The Computer History Museum has manuals and other assorted documentation for each version available on its website.
Note, however, that this source code release does not mean CP/M is open source. The code is being offered for educational purposes only and no commercial use is allowed.
If, on the other hand, you'd just like to play around with a machine running CP/M, you can try Stefan Tramm's web-based Intel 8080 emulator, here.
Various other emulators for running the OS on your own hardware can be found around the web, and there's also Tim Olmstead's unofficial CP/M software archive, here. ®